Because quite often the data in your pick and place file is not accurate
enough
to do the job properly.

Here's an article that explains why:

http://www.frontdoor.biz/China2005/ResolvingComponentPolarityProblems.pdf

If you are creating polarized part footprints in your library in random
orientations
(which your CAD system will define as zero degrees), and then ROTATE them
in your design, the pick and place file will list all of the end-result
rotations
of each kind of footprint, but the vendor still has no idea what your ZERO
was,
so they have to rely on some type of visual reference to make sure they are
mounting the component correctly. Since some people do it differently than
the standard, they pretty much have to check EVERYTHING.

You can't just say "use the data" unless the data is reliable.
The article explains it a lot better than that last paragraph.
Check it out...

Jack




On 3/21/07, Matthew Lamkin <[log in to unmask]> wrote:
>
> Why?
>
> Why does it matter to you guys where pin 1 is?
>
> to me it's only an internal numbering system used only by Cadstar and has
> no relevance
> outside of my CAD data.
> It does not get used as pin 1 once I create Gerber files and does not get
> used by any placement machines
> we have.
>
> Our placement machines take it's data from the Gerber files rather than
> any cad data from the pcb program.
> And we take it from the Gerber's because we can have a panel full of data
> including all the fiducials etc.
>
> So what is it that makes pin 1 so important to you all?
>
> Cheers,
> Matthew.
>
>
>
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